Spurious velocities in lattice Boltzmann

Stationary droplets simulated by multi-phase lattice Boltzmann methods lead to spurious velocities around them. In this article I report the origin of these spurious velocities for one example and show how they can be avoided.Comment: 4 pages, 1 figure, to be presented at the 11th international conference on discrete fluid dynamics (2002

Interpreting Sustainability in Economic Terms: Dynamic Efficiency Plus Intergenerational Equity

Economists have expended considerable effort to develop economically meaningful definitions of the somewhat elusive concept of “sustainability.” We relate such a definition of sustainability to well known concepts from neoclassical economics, in particular, potential Pareto improvements (in the Kaldor-Hicks sense) and inter-personal compensation. In the inter-temporal realm, we find that dynamic efficiency is a necessary but not sufficient condition for a notion of sustainability that has normative standing as a goal for public policy. We define sustainability as dynamic efficiency plus intergenerational equity. Further, we argue that it is not unreasonable for economists to focus on the efficiency element, leaving equity considerations to the political process. The analogy to the relationship between potential Pareto improvements and (intragenerational) transfers can facilitate discussions about sustainability, both within the economics community and as part of an interdisciplinary discourse, and makes the basic concepts easier to operationalize.

Robust estimates of exporter productivity premia in German business services enterprises

A large and growing number of micro-econometric studies show that exporting firms are more productive than firms that sell their products on the home market only. This so-called exporter productivity premium qualifies as a stylized fact. Only recently researchers started to look at the role of extreme observations, or outliers, in shaping these findings. These studies use micro-econometric methods that are robust against outliers to show that very small shares of firms with extreme values drive the result. The large exporter productivity premium found for samples of firms including outliers are dramatically smaller in samples without these extreme observations. Evidence on this, however, is limited so far to firms from manufacturing industries. This note adds comparable evidence for firms from the business services industries. We find that the estimated exporter productivity premium is statistically significant and relevant from an economic point of view when a standard fixed effects estimator is used to control for unobserved firm characteristics, but that it drops to zero when a robust estimator is applied.Exporter productivity premium, services firms, robust estimation, panel data